1. Field of the Invention
The present invention generally relates to a pixel structure and a liquid crystal display panel having the pixel structure, in particular, to a liquid crystal display panel and a pixel structure thereof, which can alleviate color shift of image.
2. Description of Related Art
The thin film transistor liquid crystal display (TFT-LCD) is becoming the mainstream in the display market because of its superior characteristics, such as high image quality, high space utilizing efficiency, low power consumption and no radiation etc. Recently, high contrast ratio, fast response time and wide viewing angle are the major demands. In order to reach the achievement, a multi-domain vertically alignment (MVA) TFT-LCD is proposed.
FIG. 1 is a schematic, cross-sectional view showing a conventional MVA TFT-LCD. Referring to FIG. 1, the liquid crystal display panel 100 includes a thin film transistor array substrate 110, a color filter substrate 120 and a liquid crystal layer 130. By means of the protrusions 140 or slit patterns (not shown) formed on the thin film transistor array substrate 110 and the color filter substrate 120, when an electric field is applied between the substrates 110 and 120, the liquid crystal molecules 132 in the liquid crystal layer 130 are rearranged along different orientations to thereby define a four-domain (4 domain) distribution and thus achieve the effect of the wide viewing angle.
Although the MVA TFT-LCD or a horizontal alignment TFT-LCD can achieve the purpose of the wide viewing angle, users still encounter color washout when viewing an image thereon from different viewing angles.
FIG. 2 shows gamma (γ) curves of a conventional MVA TFT-LCD in different viewing angles (θ), (φ=0). Referring to FIG. 2, the ordinate represents the brightness, and the abscissa represents the gray level. As shown in FIG. 2, the larger viewing angle, the worse distortion of the gamma curve, that is, the color shift of image becomes aggravating. The color shift occurs in a large viewing angle when the middle and the low gray level has a higher brightness. Therefore, an efficient method for solving the color shift of image is to decrease the brightness of the middle and the low gray level. The US patent publication No. 2005/0030439 discloses a design of dividing a pixel into two sub-pixels.
FIG. 3 is a schematic, the top view showing a conventional thin film transistor array substrate. Referring to FIG. 3, a first pixel electrode 190a and a second pixel electrode 190b are located in a left region and a right region of a pixel structure 190, respectively. The first pixel electrode 190a is electrically connected to a drain 175 via a contact hole 181. The drain 175 extends underneath to the second pixel electrode 190b. A voltage applied to the second pixel electrode 190b undergoes a voltage drop by the capacitance coupling effect, thus the voltage applied to the second pixel electrode 190b is smaller than that applied to the first pixel electrode 190a. Thereby, the region of the second pixel electrode 190b is darker than that of the conventional one in the middle and the low gray level, while the brightness of the region of the first pixel electrode 190a is similar to that of the second pixel electrode 190b. Therefore, the pixel structure 190 can solve the problem of color shift of image in a large viewing angle.
However, complying with the optimistic response time and the transmittance of various panels with different scales and resolutions, the gap between the protrusions or slits is limited, and the adjustment for the area ratio of the first pixel electrode 190a to the second electrode 190b is accordingly restricted.
In addition, the pixel structure 190 corresponds to the same thin film transistor; the voltage applied to the first pixel electrode 190a and the second pixel electrode 190b respectively are different, which aggravates the flicker phenomenon of the frame.
FIG. 4 is a schematic, the top view showing a color filter substrate corresponding to the thin film transistor array substrate in FIG. 3. Referring to FIG. 3 and FIG. 4, the drain 175 is opaque as being made of metal. In order to avoid the aperture ratio of the pixel structure 190 is decreased; the drain 175 must be disposed corresponding to the protrusion 272, as shown in FIG. 4. However, if an assembly shift occurs in the fabrication of the panel, wherein the drain 175 is not exactly corresponding to the protrusion 272, the aperture ratio of the panel is affected due to the exposure of the drain 175.